Angelina Jolie's Salt Trainer: "She Can Be Stubborn!"

Angelina Jolie is one of the biggest stars in the world -- but that doesn't mean her Salt stunt trainer didn't tease her.

"We often used to joke about making her suffer, especially when wearing a harness," Simon Crane tells Self magazine of working with Jolie on the new action thriller, out Friday. "She wouldn't show me the bruises from that!"

And tough Jolie, 35, did sustain a minor injury while making the flick.

"During her final fight Liev [Schrieber]...She had to dive through an opening door firing a gun...as she carried the sequence on, she rushed into a corner piece of a set and bumped her head," Crane recounts.

The fight sequence was delayed, and Jolie took "a precautionary trip to the hospital -- arguing against it all the way...she can be stubborn!"

Crane has worked with Jolie on numerous films and says the veteran action star does 99% of her own stunts, occasionally using a stunt double, Eunice. To prep for fight scenes as Evelyn Salt, "we got her learning a combination of Muay Thai and Krav Magha," for two-hour sessions three or four times a week, Crane explains.

He adds: "One of the important issues was to bring her body and mind up to a level of fitness that would enable her to take on same of the physical pressures of Salt.

Her Salt-y diet? "She has to have 70% carbohydrates and 30% protein diet with an anaerobic training regime as opposed to aerobic, so she can put muscle on without losing weight. Sticking to four or five meals a day routine as much as possible."

And plenty of restrictions for the mom of six: "No junk food, no empty calories, and alcohol only on weekends."